In a national poll from CNN, the billionaire looks stronger than ever as he
fends off attacks from Marco Rubio and Ted Cruz

Donald Trump looked set to storm to a runaway lead in the race for the Republican presidential nomination as 11 states prepared to vote on "Super Tuesday".

The prospect of Mr Trump becoming the party's nominee forced his opponents into increasingly frantic and toxic attacks amid warnings such a result could irrevocably split the conservative movement in America.

In a sign of confidence Mr Trump decided to spend Super Tuesday campaigning in three states - Ohio, Kentucky and Florida - that are not even voting until later this month.

To win the Republican nomination Mr Trump needs 1,237 delegates. The delegates are awarded by the states according to the results of the popular vote. On Super Tuesday, a total of 595 delegates are awarded.

With four other states having already voted in February, Mr Trump had 82 delegates, Mr Cruz 17, and Mr Rubio 16.

Mr Cruz said: "Donald Trump, you're better than this. We should all agree racism is wrong, the Ku Klux Klan is abhorrent."

A host of state governors and members of Congress lined up behind Mr Rubio, who admitted he was the "underdog".

The 44-year-old senator hoped to win one state, probably Minnesota, on Tuesday and finish second in most.

He would then stake his whole campaign on winning his home state of Florida on March 15.

The only Super Tuesday state where someone other than Mr Trump had a clear poll lead was Texas. Mr Cruz led there and his campaign accepted if he failed to win it his run would be over. He also hoped to win Arkansas.

Mr Rubio abandoned his previous focus on policy, making a conscious decision to stoop to Mr Trump's level of playground-style taunting.

His campaign said Mr Rubio accepted he had to "become part of the circus" to defeat Mr Trump. One aide said it was the "price of admission" to get his speeches covered live on television like Mr Trump's.

He accused the property mogul of "wetting his pants" in a televised debate, having the "worst spray tan in America," flying around on "Hair Force One" and being unable to spell.

The senator said Mr Trump had "small hands" and added: "You know what they say about men with small hands...you can’t trust 'em!"

He also called Mr Trump a "world class con artist who is trying to pull off the biggest scam in American political history".

Mr Cruz claimed Mr Trump was refusing to publish his tax returns because they could show links to the mafia.

At a massive football stadium rally in Madison, Alabama, where he claimed the audience numbered 32,000, Mr Trump said: "I'm not a con artist. I built a great company." He called Mr Rubio a "baby" and Mr Cruz a "liar".

To roars from the crowd he added: “I hate to say it, but I’m becoming mainstream."

Mr Rubio compared his opponent to Kim Jong-un.

He said: "There is a lunatic in North Korea with nuclear weapons, and some would say a lunatic trying to get hold of nuclear weapons in America."

Emboldened by predictions of a sweeping win Mrs Clinton began looking ahead to a potential general election fight against Mr Trump.

Donald won't make America great again, he'll make America orange.

Marco Rubio

Allies of the former secretary of state have begun requesting information about the billionaire's business dealings from state governments, reviewing court filings relating to his companies, and conducting polls totest lines of attack.